This invention relates to a heat treatment jig (CVD coated products) with a silicon carbide coating for production of a semiconductor which is used for a heat treatment process in production of a semiconductor such as, for example, a susceptor or a wafer boat and a method of producing the heat treatment jig.
Conventionally, CVD coated products are used as heat treatment jigs such as a susceptor or a wafer boat. A CVD coated product is produced by forming a film of silicon carbide (hereinafter referred to as CVD-SiC film) on the surface of a base material by a chemical vapor deposition method (hereinafter referred to as CVD method), that is, by providing a coating on the surface of a base material
As such heat treatment jigs, the first to third prior art heat treatment jigs described below are available.
First, the first prior art heat treatment jig will be described with reference to FIG. 6.
FIG. 6 is a schematic view showing part of a section of the heat treatment jig of the first prior art taken in a direction of the thickness of a CVD-SiC film.
In the CVD-SiC film 22, crystal of silicon carbide continuously grows linearly or radially from a surface 1a of a base material 1 toward the surface of the CVD-SiC film 22.
Subsequently, the second prior art heat treatment jig will be described. This heat treatment jig is formed by performing coating by a plurality of times, that is, by forming a plurality of CVD-SiC films on the surface of a base material. The construction of the CVD-SiC film of the second prior art heat treatment jig is substantially similar to that of the first prior art heat treatment jig. It is to be noted that, in FIG. 6-8, a stroke of impurity dispersion which occurs from a start point provided by the base material is schematically indicated by an arrow mark 23.
FIG. 7 is a schematic view showing part of a section of the CVD-SIC film of the heat treatment jig of the second prior art taken in a direction of the thickness. In the CVD-SiC film 24, crystal of silicon carbide continuously grows in a direction of the thickness through a boundary 25 intermediately of the CVD-SiC film 24 of the second prior art heat treatment jig.
Subsequently, the third prior art heat treatment jig will be described with reference to FIG. 8. FIG. 8 is a schematic view showing part of a section of the heat treatment jig of the third prior art taken in a direction of the thickness of the CVD-SiC film.
This heat treatment jig is formed by grinding the surface of a substrate film (CVD-SiC film) in each of a plurality of times of coating and forming another CVD-SiC film 29 on the ground surface 28 in order to interrupt continuous growth of the CVD-SiC film 26 in the direction of the thickness. The method of compulsorily interrupting the crystal growth (face) in this manner is described in Japanese Patent Laid-Open Application No. Heisei 5-87991.
In the first prior art heat treatment jig, an impurity disperses from the base material into an adjacent position of the heat treatment jig through the CVD-SiC film 22.
In the first and second prior art heat treatment jigs described above, grain boundaries of polycrystal of silicon carbide are formed linearly in a direction of the thickness in the CVD-SiC film 22. The impurity which disperses from the base material 1 into an adjacent portion of the heat treatment jig through the CVD-SiC film 22 advances fastest through grain boundaries of polycrystal of silicon carbide as indicated by an arrow mark in FIG. 6. Accordingly, diffusion of an impurity takes linear strokes. In order to retard external diffusion of the impurity, the CVD-SiC film must be covered with a thick coating.
Meanwhile, in the third prior art heat treatment jig wherein the substrate film is ground in order to suppress continuous growth of crystal, although crystal growth of the substrate film 27 can be suppressed, the impurity may possibly be attracted to and remain on the ground face 28, and this may possibly give rise to a problem that the ground face 28 provides a start point for impurity dispersion. It is to be noted that, in FIG. 8, a stroke of impurity dispersion which occurs from a start point provided by the base material is schematically indicated by an arrow mark 30, and another stroke of impurity dispersion which occurs from a start point provided by the ground face itself is schematically indicated by another arrow mark 31.
Besides, while grounding of a substrate film can be performed readily where the heat treatment jig has a simple shape, for example, like a susceptor, where the heat treatment jig conversely has a complicated (not planar) shape, for example, like a boat, the grounding operation is very difficult. Further, even where the heat treatment jig has a planar shape, there is another problem that much operation time is required by a grinding step.
Furthermore, where grounding is performed, the heat treatment jig may possibly suffer from a different problem that the adhesion strength of a film to the ground face is not sufficiently high and the film may be exfoliated by a sudden thermal hysteresis.
Thus, in order to solve the problems described above, film formation processing conditions for obtaining a heat treatment jig wherein the impurity diffusion rate can be minimized and a multiple layer film which is free from a defect and is superior in adhesion have been investigated.